The goal of this project is to identify differentially expressed genes and chromosomal regions associated with nephroblastoma formation in clonal lines of rainbow trout. Studies with lower vertebrates have made important comparative contributions to the understanding of carcinogenesis, and rainbow trout are a leading lower vertebrate carcinogenesis model. Trout are uniquely suited for this study because of their large size, their propensity to develop nephroblastomas, and the ongoing development of a good comparative map in this species. Human nephroblastomas (Wilms' tumor) arise from deviations in normal differentiation of a short-lived population of embryonic kidney precursor cells. Irregularities in the functioning of the Wilms' tumor gene (WT1), which is normally involved in kidney and gonadal development and sex differentiation, appear to play a fundamental role in the formation of this cancer, while mutations affecting other characterized tumor suppressor genes are rare. The key processes in the induction of this cancer seem to lay in aberrant differentiation, possibly involving the loss of imprinting, which includes anomalies in WT1 regulation. Trout offer an opportunity to study this in a genetically defined background of clonally derived populations. Nephroblastomas can be readily induced at low cost in this species, in this case by MNNG exposure in the genetically uniform hybrid progeny of crosses between two homozygous clonal trout lines. The project objectives include: 1) Analysis of gene expression differences between normal kidney and Wilms' tumor tissues by cDNA-subtraction Amplified Fragment Length Polymorphism (csAFLP). 2) We will simultaneously conduct genome-wide screens between kidney and nephroblastoma DNA using Amplified Fragment Length Polymorphism (AFLP) markers, which will reveal LOH and genomic deletions, as well as aberrant methylation. Linked markers will be used for isolating the corresponding trout BACs, which will be partially sequenced for identification of genes within the LOH deletion, allowing the determination of synteny with human chromosomes and identification of potential candidate tumor suppressor genes for further analysis. This project should provide fundamental insights into nephroblatoma carcinogenesis using an experimentally tractable lower vertebrate model system.